Conventional natural draft burners for direct fired heaters have air registers through which combustion air is admitted to a combustion chamber of the heater. Noise generated in the combustion chamber escapes via the air registers to environs of the heater and additional noise is generated by passage of the combustion air through the air registers. This additional noise also escapes to the environs of the heater. Further in conventional natural draft burners, fuel release devices are unshielded and they radiate additional noise which escapes to the environs of the heater.
Current environmental requirements make it necessary to add noise attenuating devices to natural draft burners, so as to limit escape of noise to the environs of the heater. Conventional noise attenuating devices limit escape of noise effectively, but they serve no other useful purpose and, therefore, they add to the cost of the furnace without benefiting thermal efficiency.
Fuels used in refineries and petrochemical plants frequently contain sufficient sulfur to present corrosion problems. One effective way to avoid sulfur corrosion in a heater is to operate the heater with its skin temperature above the H.sub.2 SO.sub.3 /H.sub.2 SO.sub.4 condensation range. However, such operation results in high heat losses from the heater to its environs and such operation cannot be maintained under all ambient conditions.